The agent of apple scab disease (Venturia inaequalis) is the most common pathogen in apple cultivation. Its ascospores are released in spring, mainly during daylight hours and triggered by rain events. To investigate the causes of diurnal rhythm of ascospore dissemination of the apple scab fungus ascospore releases were examined continuously with spore traps in the orchard and with laboratory assays. One of the spore traps was illuminated at night with different light sources in each year during 2011-2015. The laboratory assays were performed with different light sources with varying wavelengths and intensities. In field and laboratory conditions only light including infrared radiation stimulated ascospore release, but not with light in the visible spectrum only. Artificial illumination during night was correlated with an increase of up to 46 % of ascospores released overnight in the field. We proved that infrared radiation induces V. inaequalis to release its spores. This is the first report in which spore discharge could be stimulated during night under field conditions.

Four sources of Engelmann spruce and two of Douglas-fir were grown under eight different extended photoperiod regimes. Incandescent light 1 minute of every 15 at night at 270 lux was more effective than continuous incandescent at 1200 lux or intermittent fluorescent at 950 lux at preventing bud dormancy and maintaining continuous height growth.

Artificial lights may be used to delay flowering of soybean [Glycine max (L.) Merr.] cultivars. Previous research has suggested that night interruption imposed every other night would delay flowering as much as every-night interruption. Our objective was to evaluate the reproductive development of cultivars when exposed to night interruption every night compared with exposure every other night. One cultivar of each Maturity Group 00 through V was grown in the field at Ames, Iowa during 1978 and 1979. The four light treatments imposed every night or every other night included illumination with incandescent light from sunset to sunrise, 2300 to 0030 hours, 0030 to 0200 hours, or 0200 to 0330 hours. Control plots were not exposed to artificial light.

The average number of days that reproductive development was delayed beyond the control was twice as great for the every-night treatments as for the every-other-night treatments. Illumination from sunset to sunrise delayed reproductive development significantly more than the treatments of night interruption for 1.5 hours. Night interruption near the end of the dark period (0200 to 0330 hours) delayed reproductive development more than the earlier interruptions.

The results did not support the hypothesis that light treatments every other night would delay reproductive development as much as every-night interruptions. The lighting regime needed to delay reproductive development will depend on the photoperiod requirements of the cultivars and duration of the delay that is desired.

Exposure to Artificial Light At Night (ALAN) results in a disruption of the circadian system, which is deleterious to health. In industrialized countries, 75% of the total workforce is estimated to have been involved in shift work and night work. Epidemiologic studies, mainly of nurses, have revealed an association between sustained night work and a 50-100% higher incidence of breast cancer. The potential and multifactorial mechanisms of the effects include the suppression of melatonin secretion by ALAN, sleep deprivation, and circadian disruption. Shift and/or night work generally decreases the time spent sleeping, and it disrupts the circadian time structure. In the long run, this desynchronization is detrimental to health, as underscored by a large number of epidemiological studies that have uncovered elevated rates of several diseases, including cancer, diabetes, cardiovascular risks, obesity, mood disorders and age-related macular degeneration. It amounts to a public health issue in the light of the very substantial number of individuals involved. The IARC has classified shift work in group 2A of “probable carcinogens to humans” since “they involve a circadian disorganization”. Countermeasures to the effects of ALAN, such as melatonin, bright light, or psychotropic drugs, have been proposed as a means to combat circadian clock disruption and improve adaptation to shift and night work. We review the evidence for the ALAN impacts on health. Furthermore, we highlight the importance of an in-depth mechanistic understanding to combat the detrimental properties of exposure to ALAN and develop strategies of prevention.